Fluid expansion tank

ABSTRACT

An expansion tank includes a tank body mounted inside a housing forming a sump, and defining an internal expansion volume. A fluid inlet opening in the tank body is in communication with the sump and the expansion volume. A combination valve may be disposed on a lower end of the tank to control fluid flow between the sump and the expansion volume. The valve may be a combination duckbill valve and umbrella valve. Fluid enters the expansion volume through the umbrella valve when sump pressure exceeds expansion volume pressure by a first predetermined amount, and fluid exits the expansion volume through the duckbill valve to the sump when expansion volume pressure exceeds sump pressure by a second predetermined amount. The tank body may include a cover on which an inlet tube is formed.

CROSS-REFERENCE

This application is a continuation of U.S. Non-Provisional applicationSer. No. 15/846,866, filed on Dec. 19, 2017, which claims the benefit ofU.S. Provisional Application No. 62/436,154, filed on Dec. 19, 2016,both of which are incorporated by reference herein in their entirety.

BACKGROUND

This application is related to drive devices for a variety of vehicles,including ride-on mowers, stand-on mowers and walk-behind vehicles suchas snow throwers. A hydraulic fluid expansion tank is often associatedwith these drive devices and is often located external to the housingsof these drive devices. It is also known to locate the fluid expansiontank inside a housing of the drive device to prevent damage to theexpansion tank, conserve space and eliminate components such as externalfluid lines and fittings that are also susceptible to damage. Suchinternal tanks typically use a siphon system. There is a need for animproved internal expansion tank that will increase flexibility for thedrive device manufacturer and allow for reduced hydraulic fluid volume,reduced weight and reduced cost. There is also a need for an internalexpansion tank that will provide an improved system for removingentrained air from the hydraulic system.

SUMMARY

The present invention provides an improved hydraulic fluid expansiontank located in a fluid sump inside a housing of a drive device, whichmay be used in a variety of vehicle or other applications. In its mostbasic configuration, such an internal expansion tank has one simpleorifice or opening (in communication with sump) located near the bottomof the expansion tank and a vent opening at the top of the expansiontank in communication with atmosphere. As used herein, the terms “top”and “bottom,” or “upper” and “lower,” should be read with regard tonormal operation of a hydraulic drive device such as the examplesdisclosed herein. As is known, the moving components in the fluid sumpchurn air and oil together. This foamy mixture is forced into theexpansion tank while the oil-air mixture expands as the temperature ofthe drive device rises. During drive device operation and subsequentcooling, the air bubbles in the mixture are released into the upper airvolume of the expansion tank and out through the vent to atmosphere, andthe expansion tank returns oil having a lesser amount of entrained airto the sump through the orifice located near the bottom of the expansiontank.

In each embodiment described herein, the expansion tank body maycomprise a main body and a cover. In one embodiment, a simple orifice islocated near the bottom of the expansion tank, and an upper check valveis located near the top of the expansion tank. Such an arrangementpermits air to enter the expansion tank through the upper check valveduring thermal expansion, and fluid would also expand into the expansiontank through the lower orifice. Although functional, this embodiment isnot ideal, as it requires multiple temperature cycles to remove theentrained air from the oil.

In another embodiment, a pair of check valves is used, with a firstcheck valve located near the top of the expansion tank and permittingfluid flow only from the fluid sump into the expansion tank, and asecond check valve located near the bottom of the expansion tank andpermitting flow only from the tank to the sump. In an embodiment, thetwo check valves may be umbrella-style check valves. In a furtherembodiment, the upper check valve may be a duckbill style check valvethat can be installed from the exterior of the tank, and the lower valvemay be an umbrella-style check valve that can also be installed from theexterior of the tank. Both of these check valve designs are known andcommercially available, and other types of one-way or check valves couldalso be used.

In one configuration, a single duckbill-umbrella combination valve, suchas is commercially available from Minivalve International B.V., may belocated near the bottom of the expansion tank. The “umbrella” orflexible flange portion of the valve permits fluid flow into the tankduring thermal expansion and the duckbill portion of the valve permitsfluid flow from the tank to the sump as the fluid cools.

In a further embodiment, a fluid inlet tube (or riser tube) isintegrally formed in an expansion tank, the tube having an upper endopen to the internal volume or sump of the drive device and an openingat its lower end in communication with the umbrella portion of aduckbill-umbrella combination valve. The riser tube in this embodimentmay be formed in the cover. This configuration requires a slightly morecomplex expansion tank structure, but helps reduce air entrainment byallowing the oil-air mixture from the upper portion of the drive deviceinterior to enter the expansion tank through the fluid inlet tube andeventually exit through a vent at the top of the expansion tank incommunication with atmosphere. As the drive device cools, the fluid fromthe expansion tank, now having less entrained air, flows directly backinto sump through the duckbill portion of the duckbill-umbrellacombination valve.

In a further embodiment, the integrally formed riser tube serves as boththe inlet passage to the expansion tank and the outlet passage from theexpansion tank. A duckbill-umbrella combination valve is positioned atthe lower end of the riser tube to enable this 2-way flow. The umbrellaportion of the valve allows fluid to flow into the tank during thermalexpansion and the duckbill portion of the valve permits fluid to flowout of the tank and back through the riser tube to sump as the fluidcools. Entrained air in the fluid entering the expansion tank eventuallyescapes to atmosphere through a vent at the top of the expansion tank.

In a further embodiment, an expansion tank is used in connection with adrive device having a housing forming an internal sump containinghydraulic fluid, a transmission comprising a center section disposed inthe internal sump and a reduction gear train comprising a final outputgear, the final output gear mounted on an axle disposed in the internalsump and driven by the transmission. The expansion tank may be capableof receiving hydraulic fluid from the internal sump and discharginghydraulic fluid to the internal sump and may be disposed adjacent to thefinal output gear and separate from the housing, wherein the expansiontank is at least partially retained in position by contact with thecenter section.

A better understanding of the properties of the invention will beobtained from the following detailed description and accompanyingdrawings which set forth one or more illustrative embodiments and areindicative of the various ways in which the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an exemplary vehicle for use withan expansion tank in accordance with the teachings herein, with onedriven wheel and one transaxle removed for clarity.

FIG. 2 is a perspective view of an exemplary hydraulic drive device foruse with a first embodiment disclosed herein.

FIG. 3 is a top plan view of the drive device shown in FIG. 2.

FIG. 4 is a cross-sectional view of the transaxle of FIG. 2, along theline 4-4 in FIG. 3, depicting a first embodiment of an internalexpansion tank in accordance with the teachings herein.

FIG. 5 is an elevational view of the internal expansion tank of FIG. 4mounted in a housing member of a transaxle such as that shown in FIG. 2,and including an exploded view of a vent assembly for use with theexpansion tank.

FIG. 6 is an elevational view of the opposite side of the internalexpansion tank shown in FIG. 5, along with hydrostatic and gearingcomponents of a transaxle such as that shown in FIG. 2.

FIG. 7 is a perspective view of the internal expansion tank of FIG. 4.

FIG. 8 is an exploded perspective view of the internal expansion tank ofFIG. 7.

FIG. 9 is a perspective view of the internal expansion tank of FIG. 7,rotated 90 degrees about a vertical axis.

FIG. 10 is an exploded perspective view of the internal expansion tankof FIG. 9.

FIG. 11 is a perspective view of another exemplary hydraulic drivedevice for use with an expansion tank in accordance with the teachingsherein.

FIG. 12 is a top plan view of a housing of the hydraulic drive device ofFIG. 11.

FIG. 13 is a cross-sectional view of a portion of the drive device ofFIG. 11, along the line 13-13 in FIG. 12, depicting a second embodimentof an internal expansion tank in accordance with the teachings herein.

FIG. 14 is an elevational view of the internal expansion tank shown inFIG. 13.

FIG. 15 is a perspective view of the internal expansion tank of FIG. 14.

FIG. 16 is an exploded perspective view of the internal expansion tankof FIG. 15.

FIG. 17 is a perspective view of the internal expansion tank of FIG. 15,rotated 180 degrees about a vertical axis.

FIG. 18 is an exploded perspective view of the internal expansion tankof FIG. 17.

FIG. 19 is an elevational view of a third embodiment of an internalexpansion tank similar in basic form to that shown in FIG. 4, and whichcan also be mounted in a housing member of a transaxle such as thatshown in FIG. 2.

FIG. 20 is a cross-sectional view of the internal expansion tank of FIG.19, along the line 20-20 in FIG. 19.

FIG. 21 is an exploded perspective view of a cover and valve of theinternal expansion tank of FIG. 19.

FIG. 22 is a perspective view of the main body of the internal expansiontank of FIG. 19.

FIG. 23 is an elevational view of an expansion tank similar to thatshown in FIG. 19, which can also be mounted in a housing member of atransaxle such as that shown in FIG. 2.

FIG. 24 is an elevational view of a further embodiment of an internalexpansion tank similar to that shown in FIG. 19, and which can also bemounted in a housing member of a transaxle such as that shown in FIG. 2.

FIG. 25 is a cross-sectional view of the internal expansion tank of FIG.24, along the line 25-25 in FIG. 24.

FIG. 26 is an exploded perspective view of a cover and valve of theinternal expansion tank of FIG. 24.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies oneor more embodiments of the invention in accordance with its principles.This description is not provided to limit the invention to theembodiment(s) described herein, but rather to explain and teach theprinciples of the invention in order to enable one of ordinary skill inthe art to understand these principles and, with that understanding, beable to apply them to practice not only the embodiment(s) describedherein, but also any other embodiment that may come to mind inaccordance with these principles. The scope of the invention is intendedto cover all such embodiments that may fall within the scope of theappended claims, either literally or under the doctrine of equivalents.

For convenience of understanding the disclosure herein, an exemplaryvehicle 10 is shown in FIG. 1. It will be understood that other vehiclesand applications can be used in accordance with the present invention.In general, exemplary vehicle 10 includes a prime mover or engine 12powering a pair of hydraulic drive devices, here depicted as transaxles20, mounted on frame 14, each separately driving a wheel 18. Suchvehicles generally include an engine-driven apparatus such as mower deck15, which may be connected to engine 12 through a belt and pulleyassembly 13. In the exemplary vehicle configuration, two user controls16 are mounted in vehicle 10 and connected to respective transaxles 20to independently control the output speed and direction of eachtransaxle 20 to enable zero turn radius capability of vehicle 10. Onlyone of the driven wheels 18, transaxles 20 and user controls 16 isdepicted in FIG. 1 for clarity. It will be understood that there will beadditional linkages and the like that are not depicted herein for thesake of simplicity, such as engine controls and brake linkages.Additionally, methods of controlling transaxles 20 other than thatdepicted are known and may be used in connection with the inventiondisclosed herein.

The exemplary transaxle 20 is shown in more detail in FIGS. 2-6. A mainhousing 21 is joined by a plurality of fasteners 23 and joint sealant(not shown) or by other known means to a side housing 22 along a splitline generally perpendicular to output axle 24 to form a case comprisinga hydraulic fluid sump 25. It will be understood that for properoperation of the devices as disclosed herein, the drive device such astransaxle 20 should be properly sealed to prevent the introduction ofair into the fluid sump 25.

In a typical zero turn vehicle arrangement, two such transaxles 20 areused, as previously mentioned herein, and each may be a mirror image ofthe other. Hydrostatic transaxles are well-known in the art, and theinternal functioning of the various components, such as the pump, motor,hydraulic porting and the like are described, for example, in U.S. Pat.Nos. 5,314,387; 6,185,936; 7,926,624; and 7,926,266, all of which arecommonly owned with this application and all of which are incorporatedherein by reference.

Certain internal components of transaxle 20 are depicted in FIG. 6,including a hydraulic pump 41 rotatably disposed on a center section 50in sump 25 and controlled by a swash plate 42. Pump input shaft 43drives hydraulic pump 41 and may also drive an optional charge pump 48.Hydraulic motor 51 is also rotatably disposed on center section 50 insump 25 and drives a motor output shaft 44, which is engaged to areduction gear train 45 comprising a final output gear 29. As shown inFIGS. 4 and 6, the final output gear 29 can be positioned between sidehousing 22 and internal expansion tank 30. Final output gear 29 isdrivingly engaged to and supported on the output axle 24 which isrotationally supported by a proximal bearing 27 and a distal bearing 28.Except as described herein, the internal structure and operation oftransaxle 20 can be substantially identical to that shown and describedin the aforementioned U.S. Pat. Nos. 7,926,266 and 7,926,624 and thereader is referred to those patents for additional details on thestructure and operation of such hydraulic components. Alternatively, ina typical integrated hydrostatic transaxle (IHT) arrangement, such asthat shown in U.S. Pat. Nos. 5,314,387 and 6,185,936, a single transaxleunit includes two axles and housing structure surrounding and supportingthe two axles in a manner that also allows application of the presentinvention to that type of transaxle unit. Furthermore, the invention maybe applied in conjunction with the axle support structure associatedwith just one or with both of the two axles in a typical IHTarrangement, as needed.

The particular shape of the housing is not critical, but transaxlehousings generally have an axle horn such as axle horn 21 a or aseparate area within the main housing to accommodate the axle.Configuring the internal expansion tank such that at least a portion ofit encompasses the axle allows for a more compact unit. In theembodiment depicted, axle horn 21 a is integrally formed as part of themain housing but separate axle horns that are attached to a main housingare known. The size and shape of axle horn 21 a can be varied dependingon application requirements.

As shown in FIG. 5, a vent assembly 55 comprising a vent fitting 56, avent cap 57 and a vent tube 58 can be used to connect the internalexpansion tank to atmosphere and restrict entry of contaminants intoexpansion tank 30. The vent fitting 56 depicted is an SAE-style fittingadapted for insertion into a vent stem 32 a formed on main body 32 ofexpansion tank 30, the vent stem 32 a comprising an opening to aninternal volume 39 of expansion tank 30. Vent fitting 56 is seated andsealed in vent stem 32 a when installed in vent port 21 b of mainhousing 21. Other vent assemblies may be used in lieu of the depictedvent assembly 55 to provide similar functionality.

A first expansion tank 30 is illustrated in FIGS. 4-10. Expansion tank30 is an assembly comprising a main body 32, a cover 34, an upper checkvalve 36 a, a lower check valve 36 b, and an optional magnet 38. Mainbody 32 and cover 34 form a tank body and are preferably composed of aweldable synthetic polymer (plastic) that can withstand the internaloperating environment of drive device or transaxle 20, and expansiontank 30 is capable of receiving the hydraulic fluid from, anddischarging hydraulic fluid to, internal sump 25. To enable this one-wayfluid circuit, cover 34 includes at least one upper fluid flow opening34 a to accommodate fluid flow into expansion tank 30, and at least onelower fluid flow opening 34 b to accommodate fluid flow out of expansiontank 30. It is preferred that the fluid level 25 a in the internalvolume 39 of expansion tank 30 remains above the lower check valve 36 bas it rises and falls, so that air is not pulled into sump 25.

The upper check valve 36 a is installed on the inner surface of cover 34in conjunction with upper fluid flow opening(s) 34 a, and the lowercheck valve 36 b is installed on the outer surface of cover 34 inconjunction with lower fluid flow opening(s) 34 b. Simple, low-cost,umbrella-style check valves 36 a, 36 b are shown, but other check valvesproviding the same one-way fluid flow function could be used. In analternative embodiment (not shown), removable parts comprising thesefluid flow openings or passages 34 a, 34 b can be preassembled withrespective check valves 36 a, 36 b to form two check valve/fluid passagesubassemblies that can be sealingly snap-fit or otherwise removablyinstalled into the outer surface of cover 34 to enable serviceability ofa thus modified expansion tank 30. In addition to snap-fitting thesecheck valve/fluid passage subassemblies into the cover 34, expansiontank 30 can be configured as an entirely snap-fit, non-welded assembly,wherein main body 32 and cover 34 are also sealingly snap-fittedtogether. Furthermore, the optional magnet 38 can be snap-fit onto post34 c, with the end result being an entirely snap-together expansion tankassembly 30 that does not require bonding or elastomeric seals.

Referring to FIGS. 5 and 6, expansion tank 30 includes an alignmentextension 32 b that is captured between center section 50 and mainhousing 21 to help locate and retain the expansion tank 30. Alignmentextension 32 b includes an alignment opening 32 c that engages aprotrusion 21 c formed on main housing 21 to further ensure properlocation of expansion tank 30. In addition to these locating features,main body 32 includes a housing interface form 32 d and a plurality ofhousing contact ribs 32 e that also serve to locate and preventexcessive movement of expansion tank 30. Additionally, the contact ribs32 e serve to offset the expansion tank 30 from main housing 21 to allowmore thermal transfer from sump 25 to atmosphere. These various featuresare designed to secure expansion tank 30 such that an axle clearanceopening 30 a that extends through the assembled expansion tank 30 isapproximately aligned concentrically and axially with axle opening 21 dformed through the axle horn 21 a. Securing expansion tank 30 isnecessary to prevent damaging contact of expansion tank 30 with rotatingcomponents such as output axle 24 and final output gear 29, and also toprevent impact damage or abrasion against main housing 21 and otherinternal components such as center section 50. The optional magnet 38 issecured on post 34 c in pocket 34 d proximate to the lower check valve36 b to trap ferrous particles both inside and outside of expansion tank30.

The form and details of expansion tank 30 are most clearly seen in FIGS.7-10. The main body 32 includes a cylindrical or conical structure 32 ghaving an opening 32 h formed therethrough to accommodate axle 24. Cover34 also includes a cylindrical or tube-like conical mating structure 34g that has an opening 34 h formed therethrough to accommodate axle 24.The mating inner rims of these two axle clearance openings 32 h, 34 h,as well as the perimeter mating profiles of main body 32 and cover 34are welded or otherwise sealingly joined during assembly to form aninternal volume 39 that is in communication with sump 25 via checkvalves 36 a, 36 b and with atmosphere via the vent assembly 55.Stiffening ribs 34 e are provided on cover 34 to improve structuralintegrity and minimize warping. Additionally, alignment pockets orbosses 34 f and mating alignment pins or posts 32 f, formed on cover 34and main body 32, also improve structural integrity and accuracy duringthe assembly process of expansion tank 30.

Sump 25 contains a volume of hydraulic fluid having some entrained airvolume, and may also have an air volume at the top depending upon thefill level in transaxle 20. To improve hydraulic performance (e.g. toensure pump 41 is immersed in hydraulic fluid) sump 25 will ideally befull (or nearly full) and a lesser, specified volume of hydraulic fluidwill also be resident in expansion tank 30 at startup. In general,entrainment of air can affect hydraulic performance and is caused byvigorous hydraulic fluid turbulence created by the moving componentsinside transaxle 20 during operation when an air volume is present insump 25. As the hydraulic fluid (including any air volume and entrainedair volume) in sump 25 heats up and expands, some of this fluid(including any air volume and entrained air volume) flows through checkvalve 36 a into expansion tank 30, thereby causing the tank fluid level25 a to rise while simultaneously forcing air out of expansion tank 30through vent assembly 55, including air that was entrained. As transaxle20 cools during lessened or ceased operations, the hydraulic fluidcontracts, thus causing some of the hydraulic fluid volume in expansiontank 30 to return to sump 25 by way of check valve 36 b and lowering thetank fluid level 25 a. Thus, hydraulic fluid substantially devoid ofentrained air is returned to sump 25. While the primary purpose ofexpansion tank 30 is to accommodate fluid expansion in transaxle 20,other benefits are realized, including the described reduction in theamount of entrained air after multiple heating/cooling cycles, and theuse of a smaller volume of hydraulic fluid in transaxle 20, creating anoperational cost savings. Flow of hydraulic fluid between sump 25 andexpansion tank 30 ceases when transaxle 20 returns to ambienttemperature or when a steady state operational temperature is achieved.

Another drive device 116 having a further embodiment of an internalexpansion tank 145 is shown in FIGS. 11-18. Expansion tank 145 functionsin the same manner and shares certain characteristics and components ofinternal expansion tank 30. A drive device such as that shown in FIGS.11-13 is found in commonly-owned U.S. Pat. Nos. 8,464,610 and 9,856,969,the disclosures of which are incorporated herein by reference. Aninternal expansion tank having a shape similar to that of internalexpansion tank 145 is described in commonly-owned U.S. patentapplication Ser. No. 15/347,136, the disclosure of which is incorporatedherein by reference.

Exemplary drive device 116, shown in FIGS. 11-13, is an IHT having afirst housing member 152 and a second housing member 154 joined viafasteners 118 to form an internal sump 120. Drive device 116 is drivenby an input pulley 132 and has two output axles 168, 170 that can berotated independently at different speeds both clockwise andcounterclockwise in order to steer a vehicle such as a snow thrower.

A vent assembly 176 is installed in a vent port 178 that also receives avent stem 145 a formed at the top of the internal expansion tank 145 sothat expansion tank 145 is in communication with atmosphere, the ventstem 145 a comprising an opening to an internal volume 139 of expansiontank 30. Vent stem 145 a is formed at the upper end of a neck 145 b thatextends upward from the main body of expansion tank 145. In the depictedembodiment, neck 145 b extends adjacent to and above a clutch assembly161 supported on a shaft 167. A projection 145 f extends from neck 145 bto interface with an internal mounting member such as center section 138(a mating portion of which is represented in phantom) to retain neck 145b in position and prevent disengagement of stem 145 a from vent port178. Center section 138 may be a hydraulic mounting member havingrunning surfaces for a hydraulic pump and motor and serves the samebasic function as the previously described center section 50. Expansiontank 145 is nested in the space between a pair (one shown) of reductiongear sets 100 comprising a pair of reduction gears 101 and a pair offinal output gears 104 that are drivingly engaged to the output axles168, 170. A tank outer profile 145 c of a portion of tank 145 closelyfollows an inner profile 154 a of the second housing member 154 to helpposition and limit movement of tank 145. As illustrated, a gap may existbetween tank outer profile 145 c and inner profile 154 a. Contact ribssimilar to contact ribs 32 e described previously herein can be added tostabilize tank 145 while maintaining an offset from second housingmember 154 to provide more thermal transfer from sump 120 to atmosphere.Optionally, these profiles or a portion thereof may be nominally thesame to help restrain tank 145. An inner profile 145 d of a portion oftank 145 curves around a gear spacer 124 mounted on a jack shaft 102.Gear spacer 124 maintains separation between the pair of reduction gears101 that are also mounted on and supported by jack shaft 102. Expansiontank 145 also includes at least one external support rib 145 e (threeshown) that interfaces with an output axles support structure 155 tofurther position and support tank 145.

As shown in FIGS. 14-18, expansion tank 145 is an assembly comprising amain body 146 and a cover 147 forming a tank body, an upper check valve136 a, and a lower check valve 136 b. Main body 146 and cover 147 arepreferably composed of a weldable plastic that can withstand theinternal operating environment of drive device 116, and expansion tank145 is capable of receiving hydraulic fluid from, and discharginghydraulic fluid to, internal sump 120. To enable this one-way fluidcircuit, cover 147 includes at least one upper fluid flow opening 147 ato accommodate fluid flow into expansion tank 145, and at least onelower fluid flow opening 147 b to accommodate fluid flow out ofexpansion tank 145. In the illustrated embodiment, the upper and lowerfluid flow openings 147 a, 147 b comprise an array of three smallopenings associated with each umbrella-style check valve 136 a, 136 b.As in the previous embodiment, it is preferred that the fluid level 120a in the internal volume 139 of expansion tank 145 remains above thelower check valve 136 b as it rises and falls, so that air is not pulledinto sump 120.

The upper check valve 136 a is installed on the inner surface of cover147 in conjunction with upper fluid flow opening(s) 147 a, and the lowercheck valve 136 b is installed on the outer surface of cover 147 inconjunction with lower fluid flow opening(s) 147 b. Simple, low-cost,umbrella-style check valves 136 a, 136 b are shown, but other checkvalves providing the same one-way fluid flow function could be used.

Stiffening ribs 146 a are provided on main body 146 to improvestructural integrity and minimize warping. Stiffening ribs 147 c arealso provided on cover 147 for the same purpose. The stiffening ribs 146a, 147 c also facilitate ease of assembly of expansion tank 145 andserve as baffles to reduce sloshing. In the embodiment shown, aperimeter profile 146 b of main body 146 joins with a mating groove 147e formed along the perimeter profile 147 d of cover 147 for the assemblyand welding (or otherwise joining and sealing) of expansion tank 145.

In an alternative embodiment (not shown), expansion tank 145 can beconfigured as an entirely snap-fit, non-welded assembly, wherein mainbody 146 and cover 147 are sealingly snap-fitted together. Additionally,the check valves 136 a, 136 b could be preassembled onto small snap-fit,removable parts having respective fluid flow opening(s) 147 a, 147 bformed therein, to enable serviceability of a thus modified expansiontank 145.

A further embodiment of an expansion tank in accordance with theteachings herein is illustrated in FIGS. 19-22, where expansion tank 230that is similar in many respects to the previously-described expansiontank 30 and can be used in the transaxle shown in, e.g., FIG. 2.Expansion tank 230 is an assembly comprising a main body 232, a cover234, a duckbill-umbrella combination valve 237, and an optional magnet38. Like expansion tank 30, main body 232 and cover 234 are preferablycomposed of a weldable synthetic polymer (plastic) that can withstandthe internal operating environment of drive device or transaxle 20, andexpansion tank 230 is capable of receiving the hydraulic fluid from, anddischarging hydraulic fluid to, internal sump 25. Also similar to thepreviously described embodiments, expansion tank 230 comprises a ventopening 232 a in communication with a vent of the drive device that isin communication with atmospheric pressure.

A fluid inlet tube 234 i is integrally formed in the expansion tankcover 234, the fluid inlet tube 234 i having an upper end comprising afluid inlet or opening 234 a in communication with the internal volumeor sump 25 of transaxle 20 and a fluid outlet or opening 234 b at itslower end in communication with the umbrella portion (i.e. flexiblesealing flange 237 a) of a duckbill-umbrella combination valve 237. Thefluid inlet tube 234 i and flexible sealing flange 237 a allow fluidflow through opening 234 b into expansion tank 230 during thermalexpansion of the fluid and air in sump 25. It is preferred that apressure differential of 2 psi would be sufficient to open the umbrellaportion of valve 237 in such a manner. As the fluid in transaxle 20cools, the flexible sealing flange 237 a seals the opening 234 b and theduckbill portion of the combination valve 237 (comprising a duckbillstem 237 b having a fluid inlet opening 237 c in communication with theexpansion tank internal volume 239 and a duckbill fluid outlet opening237 d in communication with sump 25) allows fluid flow out of expansiontank 230 and into sump 25. It is preferred that a pressure differentialof 1 psi be sufficient to open the duckbill valve portion of valve 237during the cooling phase of the temperature cycle. Similar to the firstembodiment, it is preferred that the fluid level in the internal volume239 of expansion tank 230 remains above the combination valve 237 as itrises and falls, so that air is not pulled into sump 25 during thecooling phase of the temperature cycle. During manufacture, a specifiedvolume of oil is added to sump 25 and to expansion tank 230 to ensurethat this minimum fluid level is maintained during operation oftransaxle 20.

Like expansion tank 30, expansion tank 230 includes an alignmentextension 232 b comprising an alignment opening 232 c that engages aprotrusion 21 c formed on main housing 21. The expansion tank main body232 also includes a plurality of housing contact ribs 232 e that serveto locate and prevent excessive movement of expansion tank 230. Theselocating features serve to secure expansion tank 230 such that an axleclearance opening 230 a that extends through the assembled expansiontank 230 is approximately aligned concentrically and axially with theaxle opening 21 d. The optional magnet 38 is secured on post 234 c inpocket 234 d proximate to the duckbill-umbrella combination valve 237 totrap ferrous particles both inside and outside of expansion tank 230.The combination valve 237 has on integral O-ring form 237 e that ispushed through a valve mounting opening 234 j formed in cover 234 duringvalve installation. The integral O-ring form 237 e secures thecombination valve 237 in the mounting opening 234 j such that theflexible flange 237 a is sealingly seated over the internal opening 234b and the duckbill opening 237 d of combination valve 237 is exposed tosump 25 on the external side of cover 234. The internal opening 234 b isconnected via fluid passage 234 m to fluid passage 234 k of theintegrally formed inlet tube 234 i, which is connected to the fluidinlet or opening 234 a.

The expansion tank main body 232 includes a cylindrical or tube-likeconical structure 232 g having an opening 232 h formed therethrough (toaccommodate axle 24) and a circular welding ridge 232 k formed thereon.Main body 232 also includes a welding ridge 232 j formed about itsperimeter. Cover 234 includes a circular weld mating surface 234 g thathas an opening 234 h formed therethrough (to accommodate axle 24) andalso includes a welding groove 234 f formed about its perimeter. Duringmanufacture, the mating weldment structures (circular welding ridge 232k and mating surface 234 g; perimeter welding ridge 232 j and perimeterwelding groove 234 f) are welded (e.g. friction welded) or otherwisesealingly joined during assembly to form the expansion tank internalvolume 239. Stiffening ribs 234 e are provided on cover 234 andstiffening ribs 232 i are provided on main body 232 to improvestructural integrity and minimize warping. An optional internal viewobstruction or barrier 232 f may be provided near the vent opening 232 ato help discourage oil addition to the expansion tank 230 duringservicing of transaxle 20 by preventing a view of the oil level. Atamper-resistant vent may also be installed on the drive device as afurther deterrent to unintentional or errant overfilling of theexpansion tank 230.

In FIG. 23, expansion tank 330 is an assembly comprising a main body232, a cover 334, a duckbill-umbrella combination valve 237, and anoptional magnet 38. Like expansion tank 230, main body 232 and cover 334are preferably composed of a weldable synthetic polymer (plastic) thatcan withstand the internal operating environment of drive device ortransaxle 20, and expansion tank 330 is capable of receiving thehydraulic fluid from, and discharging hydraulic fluid to, internal sump25. Expansion tank 330 is essentially the same as expansion tank 230,including an axle clearance opening 330 a that extends through theassembled expansion tank 330 for axle clearance, but without theintegrally formed inlet tube 234 i of cover 234. This omission mayresult in a less complex and less costly cover 334, but expansion tank330 may be less efficient at reducing entrained air. Rather than havingan upper inlet opening such as the fluid inlet or opening 234 a of cover234, cover 334 may have one or more inlet openings 334 a (one shown)formed through cover 334 directly adjacent to the flexible sealingflange 237 a.

A further embodiment of an expansion tank in accordance with theteachings herein is illustrated in FIGS. 24-26, where expansion tank 430that is similar in many respects to the previously-described expansiontank 230 and can also be used in the transaxle shown in, e.g., FIG. 2.Expansion tank 430 is an assembly comprising a main body 232, a cover434, a duckbill-umbrella combination valve 237, and an optional magnet38. Like expansion tank 230, main body 232 and cover 434 are preferablycomposed of a weldable synthetic polymer (plastic) that can withstandthe internal operating environment of drive device or transaxle 20, andexpansion tank 430 is capable of receiving the hydraulic fluid from, anddischarging hydraulic fluid to, internal sump 25. Also similar topreviously described expansion tank 230, expansion tank 430 comprises avent opening 232 a in communication with a vent of the drive device thatis in communication with atmospheric pressure. Expansion tank 430 issecured in transaxle 20 such that an axle clearance opening 430 a thatextends through the assembled expansion tank 430 is approximatelyaligned concentrically and axially with the axle opening 21 d.

In this embodiment, an integrally formed riser tube 434 i serves as boththe inlet passage to the expansion tank and the outlet passage from theexpansion tank. The riser tube 434 i has an upper end comprising a fluidinlet or opening 434 a in communication with the internal volume or sump25 of transaxle 20 and a fluid outlet or opening 434 b at its lower endin communication with the umbrella portion (i.e. flexible sealing flange237 a) of a duckbill-umbrella combination valve 237. The riser tube 434i and flexible sealing flange 237 a allow fluid flow through opening 434b and into the internal volume 439 of expansion tank 430 during thermalexpansion of the fluid and air in sump 25. As the fluid in transaxle 20cools, the flexible sealing flange 237 a seals the opening 434 b andfluid flows from the internal volume 439 into fluid inlet opening 237 c,through the duckbill portion 237 b of the combination valve 237, out ofduckbill opening 237 d, through fluid passage 434 k of the riser tube434 i and back into sump 25. The same preferred pressure differentialswith regard to valve 237 described above would apply here as well, butit will be understood that the design of expansion tank 230 and cover234 in FIGS. 19-22 would demonstrate improved evacuation of theexpansion tank compared to the design of expansion tank 430 and cover434 shown in FIGS. 24-26.

The combination valve 237 has on integral O-ring form 237 e that ispushed into a groove 434 n machined or formed in an internal valvemounting pocket 434 j of cover 434 during valve installation. When thecombination valve 237 is installed in the mounting pocket 434 j, theflexible flange 237 a is sealingly seated over the internal opening 434b and the duckbill opening 237 d of combination valve 237 is exposed tothe valve mounting pocket 434 j that is in communication with fluidpassage 434 k. The internal opening 434 b is connected via fluid passage434 m to fluid passage 434 k, which is connected to the fluid inlet oropening 434 a. The optional magnet 38 is secured on post 434 c in pocket434 d proximate to the internally mounted duckbill-umbrella combinationvalve 237 to trap ferrous particles both inside and outside of expansiontank 430.

Like cover 234, cover 434 includes a circular weld mating surface 434 gthat has an opening 434 h formed therethrough (to accommodate axle 24)and also includes a welding groove 434 f formed about its perimeter.During manufacture, the mating weldment structures (circular weldingridge 232 k and mating surface 434 g; perimeter welding ridge 232 j andperimeter welding groove 434 f) are welded (e.g. friction welded) orotherwise sealingly joined during assembly to form the expansion tankinternal volume 439. Stiffening ribs 434 e are provided on cover 434 toimprove structural integrity and minimize warping.

The expansion tanks 230, 330 and 430 each benefit from the use of asingle 2-way valve (i.e. duckbill-umbrella combination valve 237) thatis always submerged in oil. This may prove advantageous as compared toan expansion tank having an upper and lower umbrella valve where theupper umbrella valve (e.g. upper umbrella valve 36 a) may at times beexposed to an air-rich mixture of oil and air in some applications.Greater air flow and reduced oil flow through the upper umbrella valvemay result in particle contamination under the flexible flange 237 a andcompromised sealing integrity which could reduce the effectiveness ofthis upper check valve. Conversely, a lower valve position may bebeneficial due to submersion in oil that may result in improved debristolerance of the flexible flange type valves described herein.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalent thereof.

What is claimed is:
 1. An expansion tank for use with a drive devicehaving a housing forming a sump containing hydraulic fluid and having avariable first pressure, the expansion tank comprising: a tank bodydisposed in the sump and defining an internal expansion volume having avariable second pressure; a fluid inlet opening defined in the tankbody; and a combination valve disposed on a lower portion of the tankbody to control fluid flow between the sump and the internal expansionvolume, the combination valve comprises a first valve that opens topermit fluid to enter the internal expansion volume from the sump whenthe first pressure in the sump exceeds the second pressure in theinternal expansion volume by a first predetermined amount, and a secondvalve that opens to permit fluid to exit the internal expansion volumeto the sump when the second pressure in the internal expansion volumeexceeds the first pressure in the sump by a second predetermined amount.2. The expansion tank of claim 1, wherein the first valve comprises anumbrella valve and the second valve comprises a duckbill valve.
 3. Theexpansion tank of claim 1, wherein the tank body further comprises amain body and a cover, the cover comprising a valve mounting openingdefined in the cover, and the combination valve is mounted on the coverto extend through the valve mounting opening to permit fluid to flowfrom the internal expansion volume through the combination valve andinto the sump.
 4. The expansion tank of claim 3, wherein the fluid inletopening is defined in a lower portion of the cover adjacent to thecombination valve to permit fluid flow from the sump through the fluidinlet opening and the combination valve and into the internal expansionvolume.
 5. The expansion tank of claim 1, wherein the tank body furthercomprises a main body and a cover, and wherein the cover comprises afluid tube having a first, upper end open to the sump and a second,lower end open to the internal expansion volume.
 6. The expansion tankof claim 5, wherein the cover comprises an internal valve mountingpocket and the combination valve is disposed on the cover such that theinternal valve mounting pocket seals the combination valve internallywithin the tank body.
 7. The expansion tank of claim 6, wherein thefirst valve comprises an umbrella valve and the second valve comprises aduckbill valve.
 8. The expansion tank of claim 5, further comprising amagnet disposed on the cover and adjacent to the combination valve. 9.The expansion tank of claim 5, wherein the main body further comprisesan upwardly extending vent stem in fluid communication with atmosphericpressure.
 10. The expansion tank of claim 5, further comprising aplurality of stiffening ribs formed on an internal surface of the cover.11. A hydraulic drive device, comprising: a housing forming an internalsump for hydraulic fluid and having a variable first pressure; atransmission disposed in the sump; a tank body disposed in the sump andcomprising a main body and a cover engaged thereto to define an internalexpansion volume having a variable second pressure; a fluid inletopening defined in the tank body, the fluid inlet opening incommunication with the sump and the internal expansion volume; and acombination valve disposed on a lower end of the cover to control fluidflow between the sump and the internal expansion volume, the combinationvalve comprising a first valve that opens to permit fluid to enter theinternal expansion volume from the sump when the first pressure in thesump exceeds the second pressure in the internal expansion volume by afirst predetermined amount, and a second valve that opens to permitfluid to exit the internal expansion volume to the sump when the secondpressure in the internal expansion volume exceeds the first pressure inthe sump by a second predetermined amount.
 12. The hydraulic drivedevice of claim 11, wherein the first valve comprises an umbrella valveand the second valve comprises a duckbill valve.
 13. The hydraulic drivedevice of claim 12, wherein the cover comprises a valve mounting openingdefined in the cover, and the combination valve is mounted on the coverto extend through the valve mounting opening to permit fluid to flowfrom the internal expansion volume through the duckbill valve and intothe sump.
 14. The hydraulic drive device of claim 12, wherein the fluidinlet opening is defined in a lower portion of the cover adjacent to thecombination valve to permit fluid flow from the sump through theumbrella valve and into the internal expansion volume.
 15. The hydraulicdrive device of claim 12, wherein the cover comprises a fluid tubehaving a first, upper end open to the sump and a second, lower end opento the internal expansion volume.
 16. The hydraulic drive device ofclaim 15, wherein the cover comprises an internal valve mounting pocketand the combination valve is disposed on the cover such that theinternal valve mounting pocket seals the combination valve internallywithin the tank body.
 17. The hydraulic drive device of claim 16,wherein the umbrella valve opens to permit fluid to enter the internalexpansion volume, via the fluid tube, from the sump when the firstpressure in the sump exceeds the second pressure in the internalexpansion volume by the first predetermined amount, and the duckbillvalve opens to permit fluid to exit the internal expansion volume, viathe internal valve mounting pocket and the fluid tube, into the sumpwhen the second pressure in the internal expansion volume exceeds thefirst pressure in the sump by the second predetermined amount.
 18. Thehydraulic drive device of claim 15, wherein the main body and the coverdefine an opening to accommodate an output axle of the hydraulic drivedevice extending through the tank body.
 19. The hydraulic drive deviceof claim 15, wherein the main body further comprises an upwardlyextending vent stem in fluid communication with atmospheric pressure.20. An expansion tank for use with a drive device having a sumpcontaining hydraulic fluid and having a variable first pressure, theexpansion tank comprising: a tank body disposed in the sump andcomprising a main body and a cover engaged thereto to define an internalexpansion volume having a variable second pressure; a fluid inletopening defined in the tank body, the fluid inlet opening incommunication with the sump and the internal expansion volume; and acombination valve disposed on a lower end of the cover to control fluidflow between the sump and the internal expansion volume, the combinationvalve comprising an umbrella valve and a duckbill valve, wherein fluidenters the internal expansion volume from the fluid inlet openingthrough the umbrella valve when the first pressure in the sump exceedsthe second pressure in the internal expansion volume by a firstpredetermined amount, and fluid exits the internal expansion volumethrough the duckbill valve and the fluid inlet opening to the sump whenthe second pressure in the internal expansion volume exceeds the firstpressure in the sump by a second predetermined amount.